Contents:

1. Understand touch sensors
2. Different types of touch sensors
① Capacitive touch sensor
② Resistive touch sensor
③ Infrared touch sensor
④ Surface acoustic wave (SAW) touch sensor
⑤ Optical touch sensor
⑥ Ultrasonic touch sensor
⑦ Suspension touch sensor
3. Whether the use of touch sensors is limited
4. Conclusion

Have you had any difficulties in selecting or applying a touch sensor? This is a common concern when designing interactive devices today. Unfamiliarity with the characteristics of touch sensors and their potential limitations can lead to unresponsive devices and affect the end user experience. But don't worry, here's what you need to know. INFINITECH will introduce the key knowledge of touch sensors in simple terms. With this guide, you will be able to grasp the basic principles of touch sensors and solve problems you may encounter.

1. Understand touch sensors

A touch sensor is a sensor that can sense the contact or proximity of an object. It is mainly used to detect whether an object is in contact with or close to its surface, and converts this physical event into an electrical signal output. The core function of the touch sensor is to recognize user input without mechanical moving parts, making human-computer interaction more intuitive and easy. Touch sensors are used in a wide range of applications, including but not limited to the touch screens of smartphones and tablets, the control panels of smart home devices, the human machine interface (HMI) of industrial devices, and touch buttons on automotive dashboards.

2. Different types of touch sensors

Understanding the principle, characteristics and advantages and disadvantages of seven common touch sensors helps to choose the most appropriate touch sensor type according to the specific application needs.

① Capacitive touch sensor

How it works: Capacitive touch sensors are the most commonly used. It detects touch based on changes in capacitance. On the capacitive touch screen, there is a grid made of conductive materials that store electrical charges. When the finger touches the screen, because the human body is also a conductor, it will absorb a part of the charge from the capacitor, which will cause a change in the value of the capacitor. The touch controller determines the position of the touch by detecting changes in these capacitance values.

Features:

High sensitivity, can detect light touch.

Support multi-touch, can identify multiple touch points.

A conductive object, such as a finger, is needed to trigger.

Can work through thin layers of materials such as glass or plastic.

Advantages:

Good user experience, fast touch response.

Strong durability, no mechanical wear problems.

Clean and easy to maintain.

Cons:

The cost is relatively high.

Sensitive to water, grease and other substances, may lead to misoperation.

In cold weather, gloves may not work properly.

Common applications:

• Smartphones and tablets: Capacitive touch screens are the current mainstream touch technology used to control various functions of the device.

• Smartwatches and other wearables: These devices are generally small and capacitive touch screens can provide a good user experience.

• Home appliances: Control panels on kitchen appliances, washing machines and other devices, using capacitive touch sensors can enhance the beauty and ease of use of products.

• Automotive dashboard and infotainment systems: Touch screen operating interfaces within the vehicle to better integrate vehicle functions.

② Resistive touch sensor

How it works: The resistive touch screen consists of two layers of transparent resistive material with a tiny gap between the two layers. When the user presses the screen, the upper and lower layers of resistive material touch together, changing the resistance in the circuit. The touch controller determines the position of the touch by measuring the change in resistance. The structure is relatively simple and the cost is low, but it is used less in modern high-end equipment.

Features:

It is sensitive to pressure and usually requires some degree of physical pressure.

Multi-touch is usually not supported.

It can be activated with any object, including a gloved finger.

Advantages:

The cost is lower.

Durable, able to work in harsh environments.

Cons:

Requires physical compression and may not be suitable for prolonged use.

The precision and sensitivity are not as good as capacitive touch screens.

There may be wear problems after long-term use.

Common applications:

• Industrial control panels: Resistive touch screens are a good choice in environments that require durability and the ability to work in a variety of conditions.

• POS terminals and ATMs: These devices often need to be used frequently in public environments, and resistive touch screens can withstand more physical wear and tear.

• Medical equipment: Resistive touch screens can still work in environments where gloves are required.

③ Infrared touch sensor

How it works: The infrared touch screen consists of a series of infrared transmitters and receivers mounted on the four sides of the screen. These components emit infrared beams to form a grid. When a finger or other object blocks a beam, the receiver detects the change and relays the information to the controller to determine the location of the touch. Does not require direct contact with the screen, suitable for large display devices.

Features:

No need to touch the screen directly, just block the infrared beam can be triggered.

Suitable for large screen applications.

Advantages:

Insensitive to ambient light.

Can work through thicker materials.

Cons:

Regular calibration may be required to maintain accuracy.

Sensitive to dust and stains.

Common applications:

• Large information kiosks and billboards: Infrared touch screens are suitable for large-size screens, such as information query terminals, billboards, etc.

• Educational tools: Interactive whiteboards in schools often use infrared technology to touch them.

④ Surface acoustic wave (SAW) touch sensor

How it works: Surface acoustic wave technology uses piezoelectric crystals to generate sound waves that travel along the surface of the glass. When the user touches the screen, part of the sound wave energy is absorbed, which changes the sound wave pattern. The touch controller detects changes in sound waves to determine the position of the touch.

Features:

Sound waves are used to detect touch locations.

Provides high resolution and clarity.

Advantages:

High accuracy.

Long service life.

Cons:

Sensitive to environmental conditions (e.g. humidity, dust).

The cost is higher.

Common applications:

• Kiosks: In kiosks in shopping malls, airports, train stations and other places, SAW touch screens are often used to provide maps, flight information, train schedules and other services.

• Vending machines: The user interface of vending machines often uses SAW touch screens, which can simplify the purchase process and make it easier for users to select items and complete payments.

• Banking and financial equipment: On bank ATMs and other self-service financial service terminals, SAW touch screens provide accurate operational feedback, ensuring that users' transaction operations are safe and reliable.

• Medical devices: Devices in medical environments, such as patient information terminals, laboratory equipment, etc., may use SAW touch screens because they are easy to clean and suitable for places with high hygiene requirements.

• Industrial control panel: The SAW touch screen is also often seen on the operating interface of industrial automation equipment, especially in industrial applications that require precise control and high reliability.

• Public display: In public places such as libraries, museums, exhibition halls, SAW touch screens are used for information query terminals or interactive display devices to provide rich content browsing and interactive experience.

• Traffic management system: In traffic management, such as bus stop, subway station information terminal, etc., SAW touch screen can provide passengers with the required route inquiry, ticketing information and other functions.

• Commercial display: Interactive digital signage, billboards, etc. used in commercial display will also use SAW touch technology, so that customers can easily interact with the advertising content.

⑤ Optical touch sensor

How it works: The optical touch screen uses cameras at the corners or edges of the screen or leds and CCDS to detect where the user is touching the screen. When the screen is touched, the image of the touch point is captured by the camera, and the location of the touch point is calculated by an algorithm.

Features:

Use the camera to capture an image of the touch point.

Support multi-touch.

Advantages:

Suitable for large size displays.

Cost effective.

Cons:

May be affected by bright light or shadows.

Good lighting conditions are required to ensure accuracy.

Common applications:

• Large touch screen: Optical touch technology is suitable for occasions that require large displays, such as conference tables, exhibition displays, etc.

⑥ Ultrasonic touch sensor

How it works: Ultrasonic touch sensors usually use Surface Acoustic Wave (SAW) technology. It works by using piezoelectric transducers to generate sound waves on the surface of the touch screen, which travel along the surface of the screen in the absence of obstacles. When the user touches the screen, the finger absorbs or scatters part of the sound wave, causing the sound wave pattern to change. The touch controller detects these changes to determine the position of the touch.

Features:

High precision and clarity.

Can provide a better user experience.

Suitable for use in public places, as they usually have a long service life.

Advantages:

High resolution and precision.

Long service life.

Insensitive to ambient light.

Cons:

Sensitive to environmental conditions (e.g. humidity, dust).

The cost is relatively high.

Maintenance can be complex.

Common applications:

• High-end equipment: Because of its high precision, ultrasonic touch technology is sometimes used in high-end consumer electronics or professional equipment.

• Public display: Ultrasonic touch technology can also be used for large displays in public areas, such as interactive advertising screens in shopping malls.

⑦ Suspension touch sensor

How it works: The floating touch sensor allows the user to operate without directly touching the screen. This technology typically uses capacitive sensing or magnetic fields to detect a finger's proximity to the screen. When the finger approaches the screen, changes in the capacitive induction or magnetic field are picked up by the sensor to determine the position of the finger.

Features:

It can be operated without touching the screen and is suitable for use in special environments.

It provides a new way of interaction and increases the diversity of the user experience.

Advantages:

You can avoid scratches and smudges on the screen.

It works even if the user wears gloves or otherwise.

Expands the possibilities of traditional touch operations.

Cons:

The technology is relatively new and may have compatibility and stability issues.

The implementation cost is high.

Users may need time to adjust to new ways of operating.

Common applications:

• Future technology concept: Floating touch technology is still developing, but its contactless nature makes it possible to use it in the future without direct contact with the screen.

• Augmented reality (AR) and virtual reality (VR) devices: Interact with virtual objects without the need for physical contact.

Each type of touch sensor has its specific advantages and limitations, and choosing the right type needs to be determined based on the specific needs of the application. For example, for applications that require high precision and multi-touch, capacitive touch sensors may be the best choice; For applications that are cost sensitive or need to operate in harsh environments, resistive touch sensors may be more suitable.

3. Whether the use of touch sensors is limited

Although touch sensors are widely used in smart phones, tablets, smart home systems and other interactive devices by virtue of their high sensitivity, fast response, easy cleaning and beautiful appearance, there are also some limitations in the use of touch sensors.

Environmental factors: Most touch sensors are sensitive to environmental conditions, such as capacitive touch screens may not work properly at extreme temperatures, while infrared or optical sensors may be affected by strong light or obstructions.

Material limitations: The surface material of the touch screen can affect its performance, for example, some materials may affect the sensitivity of the capacitive touch screen.

Power consumption: Touch sensors often require constant power supply, which can affect the endurance of battery-operated devices.

Operating limitations: In some special environments, such as wearing gloves or wet fingers, some types of touch sensors may not work properly.

Cost constraints: High-end touch sensors, such as capacitive touch screens that support high-precision multi-touch, are more expensive, which may limit their use in low-cost products.

Durability: Although many touch sensors are very durable, they can also be subject to physical damage, especially in industrial applications or public facilities, where wear and tear after long-term use can affect their performance.

Misoperation: The touch sensor can cause incorrect commands due to accidental touch or misoperation, especially if the user interface is poorly designed.

Accessibility: Touch screens may not be the most ideal way to interact with people who are visually impaired or have limited hand mobility.

Privacy protection: In some sensitive situations, such as where personal privacy is involved, it may be necessary to consider the security of touch sensor data.

Standards and certifications: Touch sensors need to comply with relevant industry standards and safety certifications, otherwise they may not be usable in some markets or applications.

4. Conclusion

While touch sensors have brought great convenience and innovative experiences to modern life, their applications are not without limits. From environmental sensitivity at the technical level to cost-benefit analysis to the design of the user experience, each type of touch sensor has its own unique advantages and disadvantages. Understanding these different aspects can help us better choose the right touch technology for a particular application's needs. As technology advances, there is reason to believe that touch sensors will become more reliable and pervasive, continuing to push the boundaries of human-computer interaction. Hopefully, with a detailed understanding of touch sensors, you can be more confident in tackling challenges in real-world applications and make informed technical decisions for future projects.